SHOULD I CHANGE "POWER STEERING PUMP PULLEY" OR JUST THE "BELT" ?

1997 Buick Riviera • 123 miles

Squealing goes away when wd40 is applied (direct to power steering pulley others are working properly ) & it comes back with a little louder squeal. Not to sure if its just the whole wheel "pulley" or if its just the belt but I doubt its the belt. What suggestions or ideas do you think this could be caused by? & If im on the right track on solving this problem. ( 97 buick riviera supercharged) 3800 II series